A biped walking robot as it is called in the art has so far been made able to walk with two legs by producing in advance data for a pre-established walking pattern (hereinafter referred to as “gait”) and actuating the legs in a controlled manner in accordance with the gait data so that the robot can bipedally walk as desired.
Such a conventional biped walking robot tends to become unstable in walking position due, for example, to floor or ground surface conditions and an error in the physical parameters of the robot itself and may then even turn over.
The stability in walking position of the robot may be improved by having the robot recognize its walking state and control its walking position in real time and without resort to the gait data. Even in this case, too, occurrence of an unanticipated surface condition lets the robot lose its regular walking position and may cause it eventually to turn over.
It has therefore been suggested to adopt what is called “ZMP (Zero Moment Point) compensation” whereby the points on the sole of a foot of the robot at each of which the composite moment of floor counterforce and gravity becomes zero are converged to a target value. Control methods for the ZMP compensation have been known including a method as described in JP 5-305583 A in which compliance control is used to converge the ZMPs to a target value and thereby to accelerate the upper body of the robot, and a method in which the locations on which the feet of the robot are being grounded are modified.
In these known control methods, the robot is sought to be stabilized by changing the angular velocity of a joint region of the robot to change the path in which it is moved. This, however, causes the respective paths of movement of such parts of the robot as its free leg ends and the position of its upper body to deviate from the gaits as gait data, thereby resulting in changes in the foot stride and the height of the free legs of the robot and also in an inclination of its upper body. Such an inclination of the upper body has been compensated for while being sensed by an inclination sensor.
In a biped walking robot constructed as mentioned above, however, not only is the compensation for the upper body required, but also it presents further problems. For example, there may be the case where the free leg landing position cannot be altered as in walking over the stepping-stones, the case where an obstacle must be passed under, or the case where an obstacle on the ground must be stepped over. Then, a change in the gait may cause a change in the foot stride or a change in the posture of the upper body and the foot, thus making the robot unable to land on the stepping stones with its free legs, or causing it to hit against the upper obstacle or to stumble over the obstacle on the ground.
With the aforementioned problems born in mind, it is an object of the present invention to provide a biped walk mobile system or apparatus as well as a walk controller and control method therefor, which can achieve walk stability without changing a path of movement for each of joint regions.